The present invention relates generally to wave springs, and more particularly to an interlaced wave spring having improved fatigue and operating characteristics.
Springs are used in a variety of mechanical applications. Numerous types of springs are known in the art and each type has certain advantages and disadvantages which affect the use of the spring. Examples of known springs are coil springs, disc springs, Belleville springs, wave washers and wave springs.
The coil spring is perhaps the best known type of spring. Coil springs are typically made from round wire by coiling wire around a mandrel at a helical pitch for a specific number of turns to provide a spring with a particular length. The ends of such springs may be finished with hook ends, for example, so that the spring may be engaged between two members. The ends may also be ground flat to provide end bearing surfaces when the spring is used in compression applications. Coil springs may be made in any length and for the most part, with any diameter of wire and are suitable for light and heavy-duty applications. An example of a heavy-duty coil spring is described in U.S. Pat. No. 1,523,225, issued Jan. 13, 1925.
Belleville washers are another type of spring and are typically stamped from sheet metal. A Belleville washer acts like a spring because it is conical in shape and has an inherent flexibility due to the conical shape. Such washers may be used in a variety of light to medium duty applications. They are expensive to produce and require special tooling and also have a tendency to invert when overloaded so their deflection characteristics change. Such a spring washer is described in U.S. Pat. No. 3,319,508, issued May 16, 1967.
Disc springs are similar to Belleville washers and are also stamped out of a sheet or strip of metal. They are expensive to produce because they require special tooling. They may be used for heavy-duty applications where they must resist and support large loads. However, when overloaded, the deflection characteristics of these springs are different from that of compression coil springs because, when overloaded disc springs have a tendency to invert and collapse.
Wave washers are also similar to Belleville washers in that they are stamped from sheet metal, but with a wave pattern formed in them. These type of washers include only a single turn. The wave pattern provides the operating length for the spring and provides a means for the washer to support loads.
The wave pattern used for wave washers has also been used in wave springs such as that described in U.S. Pat. No. 4,752,178 issued Jun. 21, 1988, which is assigned to the assignee of the present invention. As shown in this patent, a wave spring which is particularly suitable for use in retaining ring-type applications, includes one or more flat wire turns which are circularly wound and waved in a sinusoidal pattern to provide a wave spring having a predesired thickness which thickness is defined by the total number of spring turns of the spring.
The wave pattern has also been incorporated into springs wherein the spring turns have a sinusoidal shape. These type of wave springs are described in the art as "crest-to-crest" wave springs because the individual spring turns are oriented in a manner so that successive crest portions of one spring turn abut successive trough portions of each adjacent spring turn. Wave springs provide certain advantages over coil springs, primarily in terms of space-savings, because the wave spring provides the same load deflection characteristics as a coil spring but in a shorter length. Also, more precise spring loading is obtained with the use of wave springs because of their uniform waved structure.
Wave springs may be made in many different styles and shapes. The crest-to-crest wave spring described above may be modified to include opposing, flat end portions which are usually formed by gradually reducing the amplitude and frequency of the waves in the spring turns down to a constant zero level to form opposing flat shim end portions. Such a construction is aptly described in U.S. Pat. No. 4,901,987, issued Feb. 20, 1990, which patent is also owned by the assignee of the present invention.
Although useful for most applications, wave springs, like coil springs may be subject to fatigue during long cycles of loading and unloading as well as repeatedly changing loads. Fatigue may affect the usefulness of wave springs in a detrimental manner because after repeated cycles of even or uneven loading, the operating stress within the spring may increase to a level at which the metal of the spring undergoes failure. One solution to fatigue is to increase the size of the spring cross-section undergoing the loading to reduce the stress created in it under load. In the spring art, this requires using a heavier and larger wire or flat wire to form the spring. This solution is not always practical.
The present invention is therefore directed to an improved, interlaced wave spring which avoids the aforementioned shortcomings and develops new and improved performance characteristics not previously obtainable with crest-to-crest wave springs having a single thickness.
In a wave spring incorporating the principles of the present invention, multiple constituent wave springs are interlaced, or interwound, together in order to effectively increase the thickness of each of the spring turns, while maintaining the spring turns in their crest-to-crest orientation and without increasing the base size of the wire used to form the spring. This interlacing results in either a reduction of the operating stress of the spring thereby increasing the fatigue life of the spring, or maintaining the operating stress of the spring while increasing the spring load. These operational parameters, and others, are affected proportionally by the number of constituent springs which make up the interlaced spring.
In an interlaced wave spring incorporating the principles of the present invention, a plurality of constituent, multiple turn crest-to-crest wave springs are combined together to form a single spring. The constituent springs are formed with equal wave patterns in which the waves have substantially the same amplitudes and frequencies so that when they are interlaced, they act together under loading as a single spring. The constituent springs may be interlaced together. When the springs are interlaced together, they are aligned so that the successive crest and trough portions of adjacent spring turns "match up" and interfit together. In one preferred embodiment of the present invention, the successive crest and trough portions of adjacent spring turns generally share the same common centerpoint. When interlaced, the wave spring's operating parameters are increased or decreased by the number of interlaced springs.
Accordingly, it is a general object of the present invention to provide a new and improved wave spring with increased beneficial spring characteristics.
It is another object of the present invention to provide a multiturn crest-to-crest compression spring with multiple, interlaced springs.
It is a further object of the present invention to provide an interlaced, crest-to-crest wave spring in which the interlacings have substantially identical wave amplitudes and frequencies.
It is still yet a further object of the present invention to provide an improved crest-to-crest wave spring which includes a plurality of crest-to-crest wave springs interlaced together such that each spring turn abuts another spring turn and whereby the crests and troughs of the waves of adjacent interlacings lie substantially adjacent to each other, thereby decreasing the operating stress in the interlaced spring.
It is still yet another object of the present invention to provide an interlaced crest-to-crest wave spring which provides the benefits normally obtained from either nesting a plurality of single-turn wave springs together or stacking a series of crest-to-crest wave springs together in series wherein the interlaced spring is formed from a plurality of flat wire strips, each of the strips being edgewound about a common edge and a longitudinal axis of the interlaced spring to define multiple wave springs, each having a plurality of spring turns, each spring turn having successive, distinct wave crest and trough portions arranged in generally sinusoidal wavepaths so that the crests portions abut the trough portions of adjacent spring turns, the plurality of springs being interlaced together such that the flat wire strips lie adjacent each other and abut each other for the length of the spring, thereby effectively increasing the thickness of the spring by the number of individual springs interwound together.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.